The present invention relates to a device and a method for determining a sample rate difference between two information signals, like e.g. between an interfered information signal and a non-interfered information signal. The device and the method for determining a sample rate difference may for example be used for improving of so-called objective measurements for the quality assessment of signals.
In applications like e.g. voice, audio and video quality measurements, there is frequently the necessity to exactly temporally align a non-interfered reference signal and an interfered test signal portion by portion. Methods which achieve this temporal alignment with a high precision are possible. For assessing the quality of encoded audio and video signals by measurement technology, today standardized perceptional measurements are used. Such a known standardized method is, for example, the so-called PESQ method (PESQ=Perceptional Evaluation of Speech Quality, PESQ(ITU-T Rec.P862)) for a correct assessment of voice or speech quality in an aurally accurate way. A frequent problem is, however, that the sample rates/frame rates of the used signals do not exactly match, as they were possibly substantially changed by the used transmission method partially on purpose, partially by tolerances. In this case, only a short section of the temporally aligned signals really matches.
With an increasing length of the portions or sections, the differences between the signals increase with respect to the sample rates/frame rates. Known quality measurement methods assess these differences as a strong interference, although a person would hardly perceive the differences. In order to correctly assess the interferences and thus to be able to execute an objective and good quality measurement, it may be necessitated to correct the sample rates before the temporal alignment of the signals. The difficulty here is, however, to determine the ratio of the sample rates of the two signals.
In known methods, this is achieved by detecting shifts of spectral components of the signals. Such a method is, for example, disclosed in patent document EP 19 189 09 A1. This method, however, necessitates very large window lengths of the signals to be examined which may, for example, be in a range of seconds in order to achieve a sufficient accuracy. Further, such a method which is based on detecting shifts of spectral components may only be applied very restrictedly, as transmission systems today usually insert additional temporal and spectral interferences into the signal. If such interferences occur during the method in an analysis window, the result is often unusable. With typical measurement sequences of a duration of for example 10 s, as they are used for example for voice quality measurement methods, thus no sufficient data is available for a reliable assessment of the sample rate or the sample rate difference. For calculating the sample rate difference, conventional methods may use the Fourier transformation.